Thermostat and method for operating in either a normal or dehumidification mode

ABSTRACT

The inventive thermostat provides for sensing the temperature and humidity within the space, and responsively controlling the operation of an air conditioning compressor and blower to maintain the desired temperature and humidity. In a first mode, the thermostat operates the compressor at maximum capacity and the blower at less than maximum capacity to provide dehumidification when the humidity level is above a set point. In a second mode, the thermostat operates the compressor and blower at maximum capacity to provide full cooling capacity when the sensed temperature is more than a predetermined amount above the desired temperature setting. The thermostat is also configured to automatically switch from the first mode of operation to the second mode of operation.

BACKGROUND OF THE INVENTION

The present invention relates to thermostats, and in particular, to thermostats used for controlling climate control systems that include a multi-stage air conditioning system.

Thermostats are used to control climate control systems to maintain the temperature of the space conditioned by the climate control system. The typical thermostat compares the sensed temperature of the space with a set point temperature and activates the climate control system to heat or cool the space to the desired set point temperature. Some climate control systems include a multi-stage cooling system that comprises a two speed compressor and a two speed indoor circulator blower. This dual speed cooling system can operate the compressor at a low speed when the demand for cooling is low, and at a high speed when the demand for cooling is high. Likewise, the indoor circulator blower may be operated at a high speed for maximum cooling or at a low speed for improved dehumidification. One method of operating a two speed system for providing optimum dehumidification is disclosed in U.S. Pat. No. 5,303,561 to Bahel, in which a mode of operating the indoor blower and compressor is described. When a thermostat senses both a room temperature and humidity level that are above the desired temperature and humidity set points, the thermostat may request the air conditioner to operate the compressor at full capacity and the indoor blower fan at less than full speed capacity. This slows the circulating air flow to allow more time for heat and moisture to be removed from the air, which provides improved dehumidification over the normal mode of operation at high speed full compressor capacity and maximum circulator blower speed. However, a thermostat providing such a dehumidification mode for operating the blower at a reduced speed will not cool the space as effectively as when the blower is at high speed. If the temperature in the space suddenly increases by several degrees as a result of doors left open, a thermostat having such a dehumidification mode will operate the air conditioner at less than full capacity and cool the space too slowly to attain the desired temperature setting and provide adequate comfort. The resulting uncomfortable temperature would consequently force the occupant to input a request to this type of thermostat to manually override the dehumidification operating mode.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, various embodiments of a thermostat for controlling a variable capacity cooling system are provided. One embodiment of a thermostat comprises a processor for receiving input signals from a temperature sensor and humidity sensor for sensing the temperature and humidity within the space, and responsively providing for operation in a first mode to operate the compressor and operate the blower at less than full capacity when the sensed temperature and sensed humidity are above the desired temperature and humidity set points, and in a second mode to operate the compressor at full capacity and the blower at full capacity when the sensed temperature is more than a predetermined amount above the desired temperature set point. The first mode of operating the compressor at maximum capacity and the blower at less than maximum capacity provides improved dehumidification when the humidity level in the space is above the desired humidity set point. The second mode of operating the compressor at maximum capacity and the blower at maximum capacity provides full cooling capacity when the sensed temperature is more than a predetermined amount above the temperature set point, regardless of whether the humidity level is above the desired humidity set point. The thermostat of the present invention automatically switches between the first mode of operation and second mode of operation as necessary to maintain the desired temperature while also offering humidity control to provide optimum comfort to the occupant.

In another aspect of the invention, a second embodiment of a thermostat is provided that comprises a processor for receiving signals from a temperature sensing means and a humidity sensing means, and for sending signals for controlling the operation of the compressor and blower, wherein the processor responsively operates the compressor at the maximum speed and operates the blower at less than the maximum speed when the sensed humidity is above the desired humidity set point and the sensed temperature is within a predetermined amount above the temperature set point. The processor also responsively operates the compressor at the maximum speed and the blower at the maximum speed when the sensed temperature is more than a predetermined amount above the desired temperature set point.

In yet another aspect of the present invention, some embodiments of a thermostat can automatically switch between a first mode of operation to provide optimum dehumidification and second mode of operation to provide maximum cooling, to prioritize holding the temperature of the space over dehumidification for maintaining optimum comfort to the occupant.

Yet another aspect of the present invention is to provide a thermostat that displays the present mode of operation of the thermostat on a display means, such that the occupant may be alerted of either a humidity level above the desired humidity set point or of a temperature more than a predetermined amount above the temperature set point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a building having an air conditioning system in connection with a thermostat according to the principles of the present invention.

FIG. 2 is a flow chart illustrating the method of operating a thermostat according to the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A thermostat for controlling a climate control system in which embodiments of the present invention can be implemented is indicated generally as 20 in FIG. 1. The climate control system includes an air conditioning system having a compressor unit 22 and a blower unit 24 each of which is capable of operating at full capacity and at less than full capacity. The thermostat 20 controls the operation of the air conditioning system via connections to a compressor motor and a blower motor. The thermostat 20 further comprises an internal or external temperature sensor 26 and an internal or external humidity sensor 28 for sensing the temperature and humidity within the space conditioned by the air conditioning system. In one embodiment, the thermostat 20 comprises a processor for receiving input signals from the temperature sensor and humidity sensor. The thermostat is also configured to enable an occupant to provide input to the processor of a desired temperature set point and a desired humidity set point. The processor of the present invention is generally a microprocessor, and is preferably a SCC825A microcontroller manufactured by Samsung, and has an RS 485 input port pin.

In response to a signal from the temperature sensor indicating a temperature that is above a desired temperature set point, a program in the processor initiates signals for controlling the activation of the compressor and blower of the air conditioning system to cool the space. Specifically, the program in the processor operates according to the flow chart shown in FIG. 2. At step 100 the processor receives input signals indicating the value of the sensed temperature T and the sensed humidity level H and stores the values in memory. The processor then compares the sensed temperature to the desired temperature set point at step 110. If the sensed temperature is not greater than the set point temperature, the processor proceeds at step 120 to decrement a counter that is used to measure the cumulative on and off running time of the air conditioner. If the sensed temperature is greater than the set point temperature, the processor proceeds to step 130 to compare the sensed humidity to the desired humidity set point. If at step 130 the sensed humidity is below the desired humidity set point, the processor proceeds at step 160 to compare the on-time counter to a default value. If at step 160 the counter is not greater than the default value, which indicates that the air conditioner had previously been running for short time periods, the processor initiates signals at step 170 for activating relays to operate the compressor at less than full capacity or low speed, and to operate the blower at full capacity or high speed. This will provide for Normal cooling capacity operation of the air conditioner. If at step 160 the counter is above the default value, which indicates that the air conditioner has been running for long time periods, the processor initiates signals at step 180 for activating relays to operate the compressor at full capacity or high speed, and to operate the blower at full capacity or high speed. This will provide for maximum cooling capacity of the air conditioner. While the air conditioner is running at steps 170 or 180, the processor compares the sensed temperature to the temperature set point at step 190. As long as the sensed temperature is not less than the set point temperature at step 190 the air conditioner will continue to run according to the preceding steps. If the sensed temperature is less than the set point temperature at step 210, the processor will discontinue operation of the compressor and blower at step 220.

If at step 130 the sensed humidity is above the desired humidity set point, the processor proceeds at step 140 to determine if the sensed temperature is more than a predetermined amount above the set point temperature. In one embodiment, the predetermined amount is about 3 degrees, but other embodiments may alternately comprise a higher predetermined amount or a selectable amount within a range of about 3 degrees to about 8 degrees. If at step 140 the sensed temperature is not more than three degrees above the temperature set point, the processor initiates signals at step 150 for activating relays to operate the compressor at full capacity or high speed, and to operate the blower at less than full capacity or low speed. This will provide for optimum dehumidification operation of the air conditioner. The processor will continue to operate in this mode until the sensed temperature at step 210 falls below the set point temperature, or the sensed temperature at step 140 rises more than three degrees above the set point temperature. If the demand for cooling is high, e.g., the doors to the space are left open to allow warm air to enter the space, the optimum dehumidification mode of operating at less than full blower speed will not provide sufficient cooling capacity to maintain the temperature in the space. In the example of a large social gathering in which the doors to the space may be left open, the temperature of the space increases at a faster rate than the blower running at reduced capacity can keep up with. .As a result, the temperature will over time increase above the set point temperature. If after a period of time the temperature rises more than three degrees Fahrenheit above the set point temperature at step 140, the processor proceeds to step 160 to switch to the Maximum cooling mode of operation. The second mode of operation overcomes the inability of the first dehumidification operating mode to maintain the temperature when demand is high, which occurs as a result of cooling at less than full capacity. Given the time that the air conditioner was running in dehumidification mode, the counter value at step 160 is accordingly above the default value, which indicates that the air conditioner has been running for a significant time period. With the counter greater than the default valve Ni, processor initiates signals at step 180 for activating relays to operate the compressor at full capacity or high speed, and to operate the blower at full capacity or high speed. This will provide for maximum cooling capacity of the air conditioner. While the air conditioner continues to run at step 180, the processor compares the sensed temperature to the temperature set point at step 190. As long as the sensed temperature is not less than the set point temperature at step 190 the air conditioner will continue to run. If the sensed temperature is less than the set point temperature at step 190, the processor will discontinue operation of the compressor and blower at step 200.

In one embodiment of a thermostat incorporating the principles of the present invention, the thermostat may also be configured to have a user adjustable counter value for adjusting the time period that the air conditioner will run at reduced capacity before switching to full cooling capacity. Likewise, the predetermined amount above the set point temperature at which the thermostat will switch from the dehumidification mode to the maximum cooling mode of operation is also user adjustable within a range. This predetermined amount may be adjusted by the user from 1 degree to 6 degrees to adjust the time period that the air conditioner will run at reduced capacity before switching to full cooling capacity.

The thermostat 100 may be configured to include an LCD display that can be used to display the mode of operation of the thermostat as either a Dehumidification mode, a Normal mode or a Maximum Cooling mode of operation. The thermostat can then display to the occupant the present mode of operation of the thermostat, such that the occupant is alerted of a humidity level above the desired humidity set point or of a temperature more than a predetermined amount above the temperature set point. Thus, the thermostat implementing the present invention can automatically switch between a first mode of operation to provide optimum dehumidification and second mode of operation to provide maximum cooling, to prioritize maintaining the temperature of the space over enabling humidity control to provide optimum comfort to the occupant.

It should be noted that the thermostat LCD display is used to display a current mode of operation and the temperature or humidity settings of the thermostat. This information may also be communicated through other display means such as a multi-color LED that changes color to indicate the mode of operation. Likewise, the inventive thermostat may not be configured to allow user adjustment of the default counter value or predetermined amount above the set point temperature. The thermostat may also be configured to be used with other apparatus not disclosed in the preceding embodiments, such as a heat pump unit in a climate control system.

Additional design considerations, readily apparent to one of ordinary skill in the art, such as the modification of the thermostat to provide adjustment of the predetermined amount or default value recited above, may also improve the user's ability to adjust or correct a cooling rate problem of the air conditioner system. It should be apparent to those skilled in the art that various modifications such as the above may be made without departing from the spirit and scope of the invention. More particularly, the apparatus may be adapted to any apparatus for cooling a space. Accordingly, it is not intended that the invention be limited by the particular form illustrated and described above, but by the appended claims. 

1. A digital thermostat for controlling the operation of an air conditioner having a variable capacity compressor and blower, comprising: a temperature sensing means for providing a signal indicating the temperature of a space, a humidity sensing means for providing a signal indicating the humidity level within the space; a processor for receiving signals from the temperature sensing and humidity sensing means and for sending signals for controlling the operation of the compressor and blower; the processor operative in a first mode to operate the compressor and the blower at less than full capacity when the sensed humidity is above the desired humidity set point and the sensed temperature is not more than a predetermined amount above the humidity set point; and the processor operative in a second mode to operate the compressor at full capacity and the blower at full capacity when the sensed temperature is more than a predetermined amount above the desired temperature set point.
 2. The digital thermostat of claim 1, wherein the processor is operative in a third mode to operate the compressor at less than full capacity and the blower at full capacity when the sensed temperature is above the temperature set point and the sensed humidity is below the desired humidity set point.
 3. The digital thermostat of claim 1, wherein the variable capacity compressor comprises a plurality of selectable speeds.
 4. The digital thermostat of claim 3, where the variable capacity blower comprises a plurality of selectable speeds.
 5. The digital thermostat of claim 3, wherein the variable capacity blower comprises a continuously variable range of speeds.
 6. The digital thermostat of claim 5, wherein the processor switches from the first mode of operation to the second mode of operation when the sensed humidity is above the desired humidity set point and the sensed temperature rises more than a predetermined amount above the temperature set point.
 7. The digital thermostat of claim 6, wherein the predetermined amount is about three degrees Fahrenheit.
 8. The digital thermostat of claim 4, further comprising a display that displays the mode of operation as Dehumidification when the blower is operating at less than full capacity and the compressor is operating at full capacity.
 9. A digital thermostat for controlling the operation of an air conditioner having a multi-speed compressor and blower, comprising: a temperature sensing means for providing a signal indicating the temperature of a space, a humidity sensing means for providing a signal indicating the humidity level within the space; a processor for receiving signals from the temperature sensing and humidity sensing means and for sending signals for controlling the operation of the compressor and blower, wherein the processor responsively operates the compressor at the maximum speed and operates the blower at less than the maximum speed when the sensed humidity is above the desired humidity set point and the sensed temperature is within a predetermined amount above the temperature set point; and wherein the processor responsively operates the compressor at the maximum speed and the blower at the maximum speed when the sensed temperature is more than a predetermined amount above the desired temperature set point.
 10. The digital thermostat of claim 9, wherein the processor operates the compressor at less than the maximum speed and the blower at the maximum speed when the sensed temperature is above the temperature set point and the sensed humidity is below the desired humidity set point.
 11. The digital thermostat of claim 9, wherein the compressor comprises at least two levels of operation.
 12. The digital thermostat of claim 9, wherein the compressor includes a motor that comprises at least two speeds of operation.
 13. The digital thermostat of claim 12, wherein the blower includes a motor that comprises at least two speeds of operation.
 14. The digital thermostat of claim 13, wherein the processor switches the blower from a less than maximum speed to the maximum speed when the sensed humidity is above the desired humidity set point and the sensed temperature rises more than a predetermined amount above the temperature set point.
 15. The digital thermostat of claim 14, wherein the predetermined amount is about three degrees Fahrenheit.
 16. The digital thermostat of claim 14, further comprising a display that displays the mode of operation as Dehumidification when the blower is operating at less than full capacity and the compressor is operating at full capacity.
 17. A digital thermostat in combination with a variable speed compressor and a variable speed blower, the combination comprising: a temperature sensing means for providing a signal indicating the temperature of a space, a humidity sensing means for providing a signal indicating the humidity level within the space; a processor for receiving signals from the temperature sensing and humidity sensing means and for sending signals for controlling the operation of the compressor and blower, wherein the processor responsively operates the compressor at the maximum speed and operates the blower at a speed that is less than the maximum when the sensed humidity is above the desired humidity set point and the sensed temperature is within a predetermined amount above the temperature set point; and wherein the processor responsively operates the compressor at the maximum speed and the blower at the maximum speed when the sensed temperature is more than a predetermined amount above the desired temperature set point.
 18. The combination of claim 17, wherein the processor switches from the first mode of operation to the second mode of operation when the sensed humidity is above the desired humidity set point and the sensed temperature rises more than a predetermined amount above the temperature set point.
 19. A method of controlling the operation of thermostat for an air conditioner having a variable speed compressor and blower, a humidity sensor and a temperature sensor, the method comprising the steps of: sensing the temperature of the space to be maintained; sensing the humidity level of the space to be maintained; determining if the sensed humidity level is above the desired humidity set point; determining if the sensed temperature is above the temperature set point but less than a predetermined amount above the temperature set point; responsively establishing operation of the compressor at full capacity and operation of the blower at less than full capacity when the sensed humidity is above the desired humidity set point and the sensed temperature is above the temperature set point but less than a predetermined amount above the temperature set point.
 20. The method of claim 19, further comprising the steps of establishing operation of the compressor at full capacity and the blower at full capacity when the sensed temperature rises more than a predetermined amount above the temperature set point. 